Hydroxylamine as an inhibitor between Z and P680 in photosystem II

Abstract

Upon addition of hydroxylamine to chloroplasts or photosystem II preparations, the EPR signal of Z ⨥ disappears and a new signal is observed. From its shape and g ‐value this signal is identified with the oxidized reaction center chlorophyll, P680 + . The decay of P680 + occurs with a halftime of ⪅ 200 μs and apparently is the result of a back reaction with the reduced form of the primary acceptor, Q A . This mode of hydroxylamine inhibition is reversible. These observations indicate that hydroxylamine, in addition to its well known inhibitory action on the oxygen evolving complex, is also able to disrupt physiological electron flow to P680 itself.